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  <title>需求</title>

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</div><hr /><div id="dba.requirements" class="section">
  <h2 class="title">需求</h2>
  <p class="para">
   The behaviour of various aspects depends on the implementation of the
   underlying database. Functions such as <span class="function"><a href="function.dba-optimize.html" class="function">dba_optimize()</a></span>
   and <span class="function"><a href="function.dba-sync.html" class="function">dba_sync()</a></span> will do what they promise for one
   database and will do nothing for others. You have to download and install
   supported dba-Handlers.
   <table class="doctable table">
    <caption><strong>List of DBA handlers</strong></caption>
    
     <thead>
      <tr>
       <th>Handler</th>
       <th>Notes</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td><em>dbm</em></td>
       <td>
        Dbm is the oldest (original) type of Berkeley DB style
        databases. You should avoid it, if possible. We do not support
        the compatibility functions built into DB2 and gdbm, because
        they are only compatible on the source code level, but cannot
        handle the original dbm format.
       </td>
      </tr>

      
      <tr>
       <td><em>ndbm</em></td>
       <td>
        Ndbm is a newer type and more flexible than dbm. It still has
        most of the arbitrary limits of dbm (therefore it is
        deprecated).
       </td>
      </tr>

      
      <tr>
       <td><em>gdbm</em></td>
       <td>
        Gdbm is the <a href="ftp://ftp.gnu.org/pub/gnu/gdbm/" class="link external">&raquo;&nbsp;GNU database
        manager</a>.
       </td>
      </tr>

      
      <tr>
       <td><em>db2</em></td>
       <td>
        DB2 is for <a href="http://www.sleepycat.com/" class="link external">&raquo;&nbsp;Oracle Berkeley
        DB 2</a>. It is described as &quot;a programmatic toolkit that
        provides high-performance built-in database support for both
        standalone and client/server applications.
       </td>
      </tr>

      
      <tr>
       <td><em>db3</em></td>
       <td>
        DB3 is for <a href="http://www.sleepycat.com/" class="link external">&raquo;&nbsp;Oracle Berkeley DB
        3</a>.
       </td>
      </tr>

      
      <tr>
       <td><em>db4</em></td>
       <td>
        DB4 is for <a href="http://www.sleepycat.com/" class="link external">&raquo;&nbsp;Oracle Berkeley DB
        4 or 5</a>. This option is available from PHP 4.3.2.  It can
        be used with BDB 5 from PHP 5.3.3.
       </td>
      </tr>

      
      <tr>
       <td><em>cdb</em></td>
       <td>
        Cdb is &quot;a fast, reliable, lightweight package for creating and
        reading constant databases.&quot; It is from the author of qmail and
        can be found at <a href="http://cr.yp.to/cdb.html" class="link external">&raquo;&nbsp;http://cr.yp.to/cdb.html</a>. Since it is
        constant, we support only reading operations. And since PHP 4.3.0
        we support writing (not updating) through the internal cdb library.
       </td>
      </tr>

      
      <tr>
       <td><em>cdb_make</em></td>
       <td>
        Since PHP 4.3.0 we support creation (not updating) of cdb files 
        when the bundled cdb library is used.
       </td>
      </tr>

      
      <tr>
       <td><em>flatfile</em></td>
       <td>
        This is available since PHP 4.3.0 for compatibility with the deprecated
        <em>dbm</em> extension only and should be avoided. 
        However you may use this where files were created in this format. That
        happens when configure could not find any external library.
       </td>
      </tr>

      
      <tr>
       <td><em>inifile</em></td>
       <td>
        This is available since PHP 4.3.3 to be able to modify php.ini files 
        from within PHP scripts. When working with ini files you can pass arrays 
        of the form array(0=&gt;group,1=&gt;value_name) or strings of the form 
        &quot;[group]value_name&quot; where group is optional. As the functions 
        <span class="function"><a href="function.dba-firstkey.html" class="function">dba_firstkey()</a></span> and <span class="function"><a href="function.dba-nextkey.html" class="function">dba_nextkey()</a></span>
        return string representations of the key there is a new function
        <span class="function"><a href="function.dba-key-split.html" class="function">dba_key_split()</a></span> available since PHP 5 which allows
        to convert the string keys into array keys without loosing <strong><code>FALSE</code></strong>.
       </td>
      </tr>

      
      <tr>
       <td><em>qdbm</em></td>
       <td>
        This is available since PHP 5.0.0. The qdbm library can be loaded from
        <a href="http://fallabs.com/qdbm/index.html" class="link external">&raquo;&nbsp;http://fallabs.com/qdbm/index.html</a>.
       </td>
      </tr>

      
     </tbody>
    
   </table>

  </p>
  <p class="para">
   When invoking the <span class="function"><a href="function.dba-open.html" class="function">dba_open()</a></span> or
   <span class="function"><a href="function.dba-popen.html" class="function">dba_popen()</a></span> functions, one of the
   handler names must be supplied as an argument. The actually
   available list of handlers is displayed by invoking
   <span class="function"><a href="function.phpinfo.html" class="function">phpinfo()</a></span> or <span class="function"><a href="function.dba-handlers.html" class="function">dba_handlers()</a></span>.
  </p>
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